Such a method is well known in the art, e.g. from the Euro-PCT Application No. 89908985.8 corresponding to U.S. Pat. No. 5,127,000 to Henrion. Therein, the network is a multipath self routing switch, so that packets may follow different paths therein and may therefore be out of sequence upon their arrival in the receiver station. In this station the packets are then resequenced based on sequence numbers constituted by time stamps allocated to them in the transmitter station.
This known resequencing method is however not applicable when the information packet stream comprises two or more types of intermixed packets which have to be in sequence in the receiver station, not only within each type they belong to but also with respect to each other. This is for instance the case with a so called Switched Multimegabit Data Service (SMDS) network as described in the Bellcore specifications TR-TSV-000772 (corresponding CCITT Draft Recommendation I364, Geneva, June 1992 or ETSI final draft pr ETS 300217 September 1992) and wherein packets belonging to a same information stream also called session or message can be transmitted either as first packets with group addresses from the transmitter station to a plurality of receiver stations, including a predetermined receiver station, via arbitrary paths, which means that they can be received out of sequence in the latter receiver station, or as second packets with individual adresses from the transmitter station to the predetermined receiver station where they are then received in sequence. As all these packets, i.e. as well the first as the second ones, belong to a same information stream, the first packets have to be resequenced in the predetermined receiver station to be in sequence not only with respect to themselves, but also with respect to the second packets. Resequencing these first and second packets with the help of sequence numbers or time stamps allocated thereto as in known systems has the important drawback that it is impossible to know upon receipt of a sequence of first and second packets whether packets have been lost, and thus whether one has to wait for those possibly lost packets.
Indeed, the transmitter station which is not aware to which message a packet belongs, has to sequentially allocate sequence numbers/time stamps to the packets it sends out, without taking into account to which message these packets belong. As a result, the packets received by a receiver station are not numbered consecutively because first packets are sent to all receiver stations, while second packets are sent to specific ones. Considering for instance a transmitter station which has to send 10 packets numbered 1 to 10 of which packets 1 to 3 are first packets, 4 to 6 are second packets intended for a first receiver station, 7 and 8 are second packets intended for a second receiver station and 9 and 10 are first packets, the first station then receives packets 1 to 6, 9 and 10 and the second station receives packets 1 to 3, and 7 to 10. The packets received are thus not numbered consecutively and it is impossible for the receiver stations to know whether the gaps in the numbering are due to packet loss or not.
To be noted that the above reasoning is also applicable to time stamps.